This manual provides the technical and service information required to
perform all forms of maintenance to the GPA—1 and GPA-la Power Amplifiers.
Section 1 covers the theory of operation and testing of the amplifier.
Sections 2,3,4.5 and 6 provide the information essential to the service
technician. Questions pertaining to unique service situations should

be referred to the Technical Services Manager at ADCOM.

Page 6

SECTION 2
SERVICE INFORMATION

Test Set—Up

A-INTRODUCTION

The GFA-l and GFA-la are unique power amplifiers in that they are a pair
of bridged amplifiers. The use of common grounds in the output system
will cause considerable problem. Testing will require a FIRST—CLASS
test set-up consisting of good equipment and good connections. SHOULD

EITHER OF THESE REQUIREMENTS FALL SHORT, NO SERVICE SHOULD BE AHMED .

Throughout the course of this manual ve strive to present the shortest
and most practical service pathway. The technician is advised to read

the manual before attempting service to assure the best use of his time.

B~EQUIPMENT '
Servicing the GPA-l series of power amplifiers will require the following
types of equipment. We have identified appropriate manufacturers and
mdels as guidelines.

1. Distortion measuring set- This device nust have/balanced
inputs. An accuracy of 0.0022 T.H.D. residual and an input capability
of at least 100 volts over a frequency range of 20 Hz to 20 kHz is needed.
We suggest the Sound Technology 1701A.

2. Volt meter- Greater than 100 kOhm per volt input sensitivity
and a minim sensitivity of 2 millivolts for both AC and DC. measurements.

The audio portion of this requirement is included in the Sound Technology